As an external cylinder of a bush type vibration absorption device, although an external cylinder made of metal has been conventionally used, an external cylinder made of resin is also employed. The resin external cylinder has a merit in that it is light in weight and can be readily molded.
In contrast, when the external cylinder is made of resin, since the strength of resin is lower than that of metal, if an extraction force is increased and the resin external cylinder is press-fit into a bracket, it is possible that the external cylinder will be damaged.
Thus, in Japanese Patent No. 3767545, in a cylindrical vibration absorption device composed of a rubber bush which has a resin external cylinder, an internal cylinder, and a rubber elastic body interposed therebetween and is press-fit into a rigid bracket, an inner surface shape of the bracket is formed in a stepped-shape by forming a recess at the inner surface of the bracket, whereas an outer surface of the external cylinder is formed in a substantially straight shape in an axial direction, the external cylinder is press-fit into the bracket while reducing the diameter of the external cylinder making use of the elastic deformation of the resin, and a step of the bracket and a step of the external cylinder are engaged with each other in the axial direction as well as in an extracting direction by an elastic restoring force after the press fit.
Further, in Japanese Patent No. 3767545, various innovations are made such that a fastening force of the external cylinder is secured by increasing a friction coefficient by making a surface of the bracket rough by subjecting the inner surface the bracket to a blast process, an engaging projection is formed at an end of the external cylinder and abutted to an end surface of the bracket so as to prevent removal, or the like.
However, the following disadvantages occur in Japanese Patent No. 3767545. That is, when the recessed section is formed at the inner surface of the bracket and when the surface is made rough, processing is time-consuming and costs are increased. Further, when the engaging projection is formed at one end of the external cylinder, the engaging projection is exposed outside of the bracket.